Lista referatów

• 2023-04-19, godz. 14:15, 5050

  Yoàv Montacute (University of Cambridge)

  TBA

• 2023-04-05, godz. 14:15, 5050

  Roland Guttenberg (TU Munich)

  Geometry of Vector Addition Systems

  We will prove the missing line conjecture for VAS. The proof proceeds in three steps, all based on the basic units of VAS: Periodic sets. 1) Prove an easy special case. 2) Explain all closure properties of classes interesting for VAS. 3) The closure properties non-trivially combine to produce a...

• 2023-03-29, godz. 14:15, 5050

  Giannos Stamoulis (LIRMM, Université de Montpellier, CNRS)

  Model Checking Disjoint-Paths Logic on Topological-Minor-Free Graph Classes

  Disjoint-paths logic, denoted FO+DP, extends first-order logic (FO) with atomic predicates dp_k[(x_1, y_1),…,(x_k, y_k)], expressing the existence of internally vertex-disjoint paths between x_i and y_i, for 1 ≤ i ≤ k. In this talk, we first show how to prove (fixed-parameter) tractability of ...

• 2023-03-22, godz. 14:15, 5050

  Wojciech Przybyszewski (MIM UW)

  Reproving combinatorial properties of nowhere-dense graphs using model theory

  A pinnacle of sparsity theory, initiated by Ossona de Mendez and Nešetřil, is the result of Grohe, Kreutzer, and Siebertz which identifies subgraf-closed classes of graphs with FPT model checking as exactly nowhere dense classes. One of the key steps in the proof is characterizing nowhere dense cl...

• 2023-03-15, godz. 14:15, 5050

  Arka Ghosh (MIM UW)

  Orbit-finite systems of inequalities

  A system of inequalities is orbit-finite if it is finite up to certain permutations of variables. In this talk, I will describe this concept using interesting examples, and present our recent results on the solvability of these systems. In particular, we have proven that the existence of finitely su...

• 2023-03-08, godz. 14:15, 5050

  Michał Skrzypczak (MIM UW)

  Binary counting is hard (for context-free grammars)

  Michaël Cadilhac recently (on Autoboz) asked the following problem: Take n > 0 and consider the alphabet A_n = { 2^i | i ≤ n }. Let L_n be the set of words over A_n that sum up to 2^n. What is the size of the minimal context-free grammar which recognises L_n? The problem is motivated by lin...

• 2023-03-01, godz. 14:15, 5050

  Florent Koechlin (LORIA)

  Two criteria to prove the inherent ambiguity of bounded context-free languages

  A context-free language is inherently ambiguous if any grammar recognizing it is ambiguous, i.e. there is a word that is generated in two different ways. Deciding the inherent ambiguity of a context-free language is a difficult problem, undecidable in general. The first examples of inherently ambigu...

• 2023-01-25, godz. 14:15, 5050

  Hugo Gimbert (CNRS, LaBRI, Université de Bordeaux)

  Martin’s proof of Borel determinacy

  Donald Martin established Borel determinacy in 1975: in every Gale-Stewart game with a Borel winning condition, either player I or player II has a winning strategy. We present Martin’s proof under a different perspective (bottom-up instead of top-down), in the special case where the winning condi...

• 2023-01-18, godz. 14:15, 5050

  Mikołaj Bojańczyk (MIM UW)

  TBA

• 2023-01-11, godz. 14:15, 5050

  Pierre Ohlmann (MIM UW)

  Memory in games and universal graphs

  I will present recent characterisations of positionality and finite memory in infinite duration games by means of universal graphs. The goal is to derive properties of games with a given objective W by understanding the structure of graphs satisfying W (meaning that all path colorations belong to W)...

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